[Standards] Expected behavior when blocking all unknown JIDs

W. Martin Borgert debacle at debian.org
Mon Jan 16 16:03:51 UTC 2017

Quoting Goffi <goffi at goffi.org>:
> Instead of blocking unconditionally unknown users (which is not an option for
> me), would not it make sense to use some kind of challenge (e.g. captcha or
> computational challenge) ? This would not block everything, but probably a
> good amount of SPAM/SPIM.

For email, there is greylisting. IIRC, the receiving server says
"try again later" on the first contact. This will be done by any
legitimate server, but for spammers holding the message for e.g.
one hour is too expensive. Any further messages will be delivered
immediately. Neither sender nor receiver notice anything, only a
one hour delay of the first message. In my experience, this
method doesn't prevent all email spam, but a large part of it.

Would this SMTP error 450/451 be applicable to XMPP?

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